This invention relates generally to the field of vehicle charging systems, and, more particularly, to an apparatus and a method for carrying out diagnostic tests on automobile alternators.
The use of automobile battery testers as a means of segregating xe2x80x9cgoodxe2x80x9d batteries (i.e., those capable of delivering and accepting adequate charge) from xe2x80x9cbadxe2x80x9d batteries (i.e., those incapable of delivering and accepting adequate charge) has become prevalent in recent years. Typically, when encountering problems with starting their automobiles, drivers suspect the battery to be the cause of the problems and immediately seek a replacement. If the battery was purchased with an accompanying warranty, the driver returns it to the battery retailer requesting an exchange of the suspect battery for a new one, on a free or prorated basis. Without proper testing, these suspect batteries are then returned to the battery manufacturer or scrap smelters where it is determined that a significant proportion are still good. This situation has resulted in substantial warranty costs to the battery retailer or the battery manufacturer and a major inconvenience to the customer.
For this reason, many manufacturers have developed automobile battery diagnostic testers for use by battery retailers and automotive service centers. These devices are intended to distinguish between good and bad batteries. Good batteries are returned to the customer for further use, often after recharging. New batteries are furnished to warranty customers only when it is determined that the returned battery is, in fact, bad and incapable of delivering or accepting adequate charge.
The use of automobile battery diagnostic testers and chargers has shown that many automotive batteries are still good but in a discharged condition. In many situations, this discharge is caused by various vehicle accessories inadvertently being left on, thus causing the depletion of battery charge and a no-start condition. In that case, the battery is adequately recharged and returned to the customer for immediate use without further starting problems.
In a properly functioning automobile, the vehicle charging system functions so that the battery is normally recharged during operation of the vehicle. To accomplish the recharge, an alternator or electric generator is used to convert a portion of the engine""s rotational mechanical energy into alternating current that is then rectified before reaching the automobile""s electrical system. The alternator, which is driven by a belt attached to an engine pulley, generates the power necessary to sustain the vehicle electrical system accessories and to replace the charge depleted from the battery during normal usage of the automobile. Failure of the vehicle charging system forces the battery to sustain the vehicle loads thus depleting its charge. Failure to recharge adequately will lead to low power, sulfation and eventual failure of the battery and, significantly, to its subsequent replacement. This can lead to expensive and bothersome multiple battery replacements before the actual cause of failure is determined. Thus, it is important that the vehicle charging system be tested when a battery is found to have charge problems.
There are a number of methods that have been developed for use in determining the effectiveness of a vehicle""s charging system. The definitive test requires removing the alternator from the vehicle, mounting the alternator on a test stand and monitoring the output of the alternator over a full range of rotation speeds and loads. This method, however, is not practical or convenient for most uses.
Another method is to test the alternator in the vehicle by measuring its voltage and current under load. Current is normally measured with a special current sensor (Hall effect) that is attached or affixed in the correct direction to the proper wires leading from the alternator. Increasing loads are imposed on the system until a maximum alternator output current is reached. Voltage is normally measured with sensors at the battery terminals, although it will be significantly affected by high charge rates.
Another method used is to measure only the battery voltage while the alternator is operating. While simple to operate, voltage sensors alone do not provide the definitive data needed to adequately determine if the vehicle charging system is fully functional, especially if the battery is discharged.
Also, a simple but dangerous method is often used. This involves disconnecting a connector cable from the battery once the engine is running and noting whether the engine quits. If it does, there is inadequate output from the alternator to handle the vehicle electrical system. Removal of a connector from the battery while in operation can cause a spark resulting in a possible explosion. Also, if the voltage regulator is faulty, high voltage can be impressed on the electrical system causing failure of its sensitive components.
Test methods of the sort described herein can produce varied results, are often cumbersome to set up and operate, are difficult to interpret and can even be dangerous. Operators must usually have special training in placement of the sensors and operation of the system.
Accordingly, despite the clear need for a highly discriminating alternator diagnostic test unit, it is believed that none of the types of test methods being used satisfy the need described herein. The situation is, of course, exacerbated by the increasing role battery retailers play in testing batteries that are serviced under warranty. The personnel responsible for dealing with battery returns have neither discriminating test units nor proper training to determine whether the battery being returned is bad or discharged simply as a result of a faulty vehicle charging system.
Furthermore, to satisfy the waiting customer a decision as to whether the battery is good or bad, and whether the vehicle charging system is operating properly, needs to be capable of being provided in a relatively short period of time.
Given the many and varied parameters that need to be addressed to allow a highly discriminating diagnostic testing regimen to take place, providing a suitable diagnostic test unit which can be used by personnel with limited training is a formidable task. Accordingly, it is a primary object of the present invention to provide a method and apparatus capable of rapidly determining whether the vehicle charging system is operating properly. A more specific object of this invention provides a test regimen capable of carrying out the appropriate determination in no more than two minutes, and still more preferably less than one minute.
Another object lies in the provision of a diagnostic test unit capable of testing various types of vehicle electrical systems having a variety of different load components while appropriately determining whether the vehicle charging system is operating properly.
Still another object of the present invention provides a diagnostic test that can be performed on the vehicle charging system without special test leads and sensor positioning.
Yet another object of the present invention provides a diagnostic test unit that can be operated safely by personnel with limited training at most.
Other objects and advantages will become apparent from the following detailed description.
In general, the present invention provides a straightforward diagnostic system and testing procedure that gives relevant data on the performance of the charging system in a battery-based electrical system.
The procedure begins by first testing the battery to determine if it has enough power to start the vehicle. If it is determined that the battery has acceptable starting capabilities, the battery is then tested to determine if it is charged sufficiently to produce an acceptable alternator test. If the battery has acceptable starting and charging characteristics, the alternator test is executed to determine the alternator charging voltage (at minimal charging current) and the alternator charging current (at minimal system voltage).
As a first step, a threshold charging voltage for the system is determined. The threshold charging voltage represents the point at which the voltage supplied by the alternator is sufficient to support a nominal vehicle electrical system load without charging the battery. Once the threshold voltage is measured, the alternator is powered by starting the vehicle and the battery is recharged briefly to replace any resultant capacity losses that occurred as a result of starting.
To determine the alternator charging current, the battery-based electronic system is loaded with increasing amounts of current from an external load until the electrical system voltage drops below the previously measured threshold voltage. At this point, the charging current generated by the alternator is determined by measuring the external load current. To determine the alternator charging voltage, the charging current is eliminated by applying an external charge current. The external charge current is adjusted until the alternator charging current is diminished and stable. The voltage of the battery-based electrical system, at this point, represents the alternator charging voltage at diminished current
The alternator charging current and alternator charging voltage are then compared with the expected values and the alternator is rated as good or bad.